Multiple level lighting systems, such as two level lighting systems, are used in various different lighting applications. For example, two level lighting systems are commonly used in overhead lighting. Such lighting systems can be used to conserve energy since they allow a portion of the lighting to be turned off when full light is not necessary.
A typical implementation of a two level lighting system includes two power switches and two ballasts, wherein each power switch in the lighting system controls only one of the ballasts in the lighting system. Turning on both of the switches at the same time powers both ballasts, thus producing full light output from the lighting system. Turning on only one of the switches applies power to only one of the ballasts in the lighting system and thus results in a reduced light level and a corresponding reduction in power consumed.
However, it is more economical to have a single ballast in the lighting system rather than two ballasts. One implementation of a two level lighting system using only a single ballast has a switch corresponding to each lamp set. Thus, this implementation requires two switches.
In an alternative implementation of a two level lighting system having a single ballast, the ballast includes two controllers, each of which controls a lamp set. In order to shut off one lamp set, the supply voltage to the controller corresponding to the one lamp set is pulled down (e.g., grounded) so that the controller is disabled. However, this implementation is not energy efficient because even though a controller is disabled, the supply voltage for that controller is still being pulled from the power supply.